1. Field of the Invention
This invention relates to speed reduction and the minimization of backlash to provide a speed reduction mechanism having high efficiency and minimal backlash and which is suitable for precision motion control applications.
2. Description of the Prior Art
Speed reduction mechanisms making use of epicyclical movements and gears having a perimeter defined by an epitrochoid curve have long been known. The magazine Design News in its Aug. 18, 1961 issue describes a single-stage cycloidal cam that forms the basis of a speed reducing mechanism. A similar structure is shown in U.S. Pat. No. 1,682,563 to Hill. Corresponding devices were previously known that made use of spur gears. U.S. Pat. No. 2,250,259 to Foote, Jr. describes such a heliocentric unit. Other related mechanisms are described in U.S. Pat. Nos. 3,429,393; 3,783,712; and 3,144,791. Some of these mechanisms incorporate two stages so that the output shaft is in line with the input shaft and rotates in the same direction. None of these patents discloses any structure for the practical elimination of backlash. The presence of backlash has been a major limitation in the application of earlier devices which, although practical for straight speed reduction applications, are not suitable for precison motion control applications where direction reversal is a requirement. For example, in positioning the arm of a robot, it is desirable to drive the arm from a high speed motor through a speed reduction unit and necessary that the arm be positioned exactly the same irrespective of the direction from which the position is approached. None of the above prior art mechanisms meets this requirement.